HDMI (High Definition Multimedia Interface) standards have already become prevailed as standards for transmitting digitized video/sound data in relation to a related-art video/sound signal transmitting system (see; for instance, Patent Document 1). Further, in relation to another video signal transmitting system, GVIF (Giga-bit Video Interface) standards have hitherto been known as standards used primarily for an in-car system (see; for instance, Patent Document 2).
Incidentally, when a digital video/sound signal is transmitted by use of a digital interface complying with the HDMI standards and the GVIF standards, transmission of the digital video/sound signal is allowed only when mutual authentication is established between a video/sound signal transmitting device and a video/sound signal receiving device by means of mutual authentication processing complying with HDCP (High-bandwidth Digital Content Protection System) specifications in order to prevent unauthorized copy of a digital signal from the viewpoint of copyright protection (see; for instance, Patent Document 3).
FIG. 8 shows an example configuration of a related-art video/sound signal transmitting system. In FIG. 8, reference numeral 80 designates a video/sound signal switching and distributing device, 20 designates a first video/sound signal transmitting device, 40 designates a first video/sound signal receiving device, and 50 designates a second video/sound signal receiving device. An HDMI interface is employed in the present example configuration as a digital interface.
The first video/sound signal transmitting device 20 has a function of outputting a digital video/sound signal in the form of an HDMI signal. The first video/sound signal transmitting device 20 also has a copyright protection function complying with the HDCP specifications. Each of the first video/sound signal receiving device 40 and the second video/sound signal receiving device 50 has a function of inputting a digital video/sound signal in the form of an HDMI signal. The first video/sound signal receiving device 40 and the second video/sound signal receiving device 50 each also have a copyright protection function complying with the HDCP specifications. The first video/sound signal receiving device 40 and the second video/sound signal receiving device 50 each additionally have a function of displaying a video and reproducing sounds for viewers from a received video/sound signal.
The video/sound signal switching and distributing device 80 is connected to the first video/sound signal transmitting device 20, the first video/sound signal receiving device 40, and the second video/sound signal receiving device 50 by way of the HDMI interface. The video/sound signal output from the first video/sound signal transmitting device 20 is output to either the first video/sound signal receiving device 40 or the second video/sound signal receiving device 50 or to both of them.
As shown in FIG. 8, when a plurality of video/sound signal receiving devices receive and display views of a video/sound signal output from a single video/sound signal transmitting device, the video/sound signal transmitting device is typically connected to each of the plurality of video/sound signal receiving devices by use of a video/sound signal switching and distributing device.
FIG. 9 is a flowchart showing example operation of the related-art video/sound signal transmitting system performed after startup of the system. In the descriptions, the first video/sound signal receiving device 40 is assumed to be receiving and displaying a view of, in an initial phase, a video/sound signal from the first video/sound signal transmitting device 20.
When the second video/sound signal receiving device 50 is connected to the video/sound signal switching and distributing device 80 (step S901) during the course of system operation (a step S900), the video/sound signal switching and distributing device 80 notifies the first video/sound signal transmitting device 20 about a change in connection status. In connection with the HDMI standards, notification is implemented by means of an HDP (Hot Plug Detect) signal. Upon receipt of then notification, the first video/sound signal transmitting device 20 cancels the connection between the first video/sound signal transmitting device 20 and the video/sound signal switching and distributing device 80 (step S902). Further, the video/sound signal switching and distributing device 80 terminates a connection to the first video/sound signal receiving device 40 (step S903).
Next, the video/sound signal switching and distributing device 80 commences mutual authentication between itself and respective devices connected thereto. Specifically, the video/sound signal switching and distributing device 80 performs mutual authentication between itself and the first video/sound signal transmitting device 20 (step S904), mutual authentication between itself and the first video/sound signal receiving device 40 (step S905), and mutual authentication between itself and the second video/sound receiving device 50 (step S906). After mutual authentication among the respective devices is completed, the video/sound signal switching and distributing device 80 notifies the first video/sound signal transmitting device 20 about completion of mutual authentication between itself and all of the devices downstream connected to the video/sound signal switching and distributing device 80 (step S907).
The first video/sound signal transmitting device 20 received an acknowledgement of completion of system startup acquires information required for authentication from the video/sound signal switching and distributing device 80, whereupon mutual authentication processing of an entire system, including the first video/sound signal transmitting device 20, is completed (step S908). From then on, the first video/sound signal receiving device 40 and the second video/sound signal receiving device 50 can receive and watch the video/sound signal output from the first video/sound signal transmitting device 20.